Three-dimensional (3D) positional audio is a technique for producing sound (e.g., from stereo speakers or a headset) so that a listener perceives the sound to be coming from a specific location in space relative to his or her head. To create that perception an audio system generally uses a signal transformation called a Head-Related Transfer Function (HRTF) to modify an audio signal. An HRTF characterizes how an ear of a particular person receives sound from a point in space. More specifically, an HRTF can be defined as a specific person's left or right ear far-field frequency response, as measured from a specific point in the free field to a specific point in the ear canal.
The highest quality HRTFs are parameterized for each individual listener to account for individual differences in the physiology and anatomy of the auditory system of different listeners. However, current techniques for determining an HRTF are either too generic (e.g., they create an HRTF that is not sufficiently individualized for any given listener) or are too laborious for a listener to make implementation on a consumer scale practical (for example, one would not expect consumers to be willing to come to a research lab to have their personalized HRTFs determined, just so that they can use a particular 3D positional audio product.